Silencing cathepsin L expression reduces Myzus persicae protein content and the nutritional value as prey for Coccinella septempunctata

Gut-expressed aphid genes, which may be more easily inhibited by RNA interference (RNAi) constructs, are attractive targets for pest control efforts involving transgenic plants. Here we show that expression of cathepsin L, a cysteine protease that functions in aphid guts, can be reduced by expression of an RNAi construct in transgenic tobacco. The effectiveness of this approach is demonstrated by up to 80% adult mortality, reduced fecundity, and delayed nymph production of Myzus persicae (green peach aphids) when cathepsin L expression was reduced by plant-mediated RNAi. Consistent with the function of cathepsin L as a gut protease, M. persicae fed on the RNAi plants had a lower protein content in their bodies and excreted more protein in their honeydew. Larvae of Coccinella septempunctata (seven-spotted ladybugs) grew more slowly on aphids having reduced cathepsin L expression, suggesting that prey insect nutritive value, and not just direct negative effects of the RNAi construct, needs to be considered when producing transgenic plants for RNAi-mediated pest control. Highlights Silencing expression of cathepsin L by RNA interference reduces protein content of Myzus persicae (green peach aphid) bodies. Honeydew of aphids with cathepsin L silenced contains elevated protein. Cathepsin L is required for efficient protein uptake from phloem sap. Aphids with cathepsin L expression silenced have increased mortality and fewer offspring. Coccinella septempunctata (seven-spotted ladybugs) grow more slowly on aphids with expression of cathepsin L silenced.